A system and method are provided for optical detection of cognitive impairment of a person using a portable video capture device (PVCD). In one embodiment, the method includes: (i) capturing video of an eye exposed to light stimuli over a predetermined time using a video camera of the PVCD; (ii) processing the video to locate at least one feature of the eye; (iii) measuring a change in the feature in response to the light stimuli; (iv) analyzing data from the measured change in the feature by extracting data from the measured change in the feature, calculating a number of parameters from the extracted data, correlating the calculated parameters with predetermined reference parameters and predicting a degree of impairment based on the results of the correlation; and (v) outputting through a user interface in the PVCD the degree of impairment to a user. Other embodiments are also described.